The present invention is directed to an air spring. More specifically, the air spring is a piston-less air spring designed to achieve a desired spring constant.
Air springs have been used for motor vehicles and various machines and other equipment for a number of years. The springs are designed to support a suspension load such as a vehicle. The air spring usually consists of a flexible elastomeric reinforced sleeve that extends between a pair of end members. The sleeve is attached to end members to form a pressurized chamber therein. The end members mount the air spring on spaced components or parts of the vehicle or equipment on which the air spring is to be mounted. The internal pressurized gas, usually air, absorbs most of the motion impressed upon or experienced by one of the spaced end members. The end members move inwards and towards each other when the spring is in jounce and away and outwards from each other when the spring is in rebound. The design height of the air spring is a nominal position of the spring when the spring is in neither jounce or rebound.
There have been two basic designs of air springs: a rolling lobe air spring, as seen in U.S. Pat. Nos. 3,043,582 and 5,954,316, and a bellows type air spring, as seen in U.S. Pat. Nos. 2,999,681 and 3,084,952. In a rolling lobe type air spring, the airsleeve is a single circular shaped sleeve secured at both ends. During jounce, the airsleeve rolls down the sides of a piston support. In a bellows type air spring, the multiple meniscus shaped portions of the air sleeve extend out radially as the spring is in jounce.
For every air spring, the spring rate is an indicator of the characteristics of the air spring. The spring rate k may be determined by the following known equation:
k=((n*Pa*(Ae)2)/V)+(Pg*(dAe/dx))
where
n=gas constant, typically 1.38,
Pa=absolute pressure,
Ae=effective area,
V=internal volume,
Pg=gage pressure,
x=height of air spring,
dAe/dx=Effective Area Rate of Change.
The effective area Ae, is determined by:
Ae=Fs/Pg
where
Fs=spring force.
For a given application, there is a specified operating pressure and target load, so the effective area for the spring is fixed.
In most applications, it is desired that the spring constant k be relatively small. In other applications, it may be desired that the spring constant be variable depending upon the operating conditions of the vehicle. For example, when encountering uneven road surfaces, if only one axle at a time responds to the uneven surface, then it is desired to have a lower spring constant. However, if multiple axles are simultaneously responding to the uneven surface, it is desired to have a higher spring constant.
The present invention is directed to an air spring wherein the spring constant of the air spring can be readily tuned to achieve a desired ride performance. Specifically, the inventive air spring has a cylindrical elastomeric sleeve, bead plates, and support rings. The sleeve is secured at each end to a bead plate. The support rings are secured to the bead beads, extending radially outward from the bead plates. The support rings have an inner shoulder, an outer shoulder, and a tracking surface extending between the shoulders. When the air spring is at design height, the sleeve contacts only the inner shoulders of the support rings.
By limiting the initial contact of the sleeve with the ring and determining where this contact occurs, the movement of the sleeve during jounce can be modified, altering the effective area rate of change.
In another aspect of the invention, the air spring and the rings may also be defined by the relationship of the sleeve hinge point and the relative location of the ring inner shoulders. Each sleeve end has a hinge point about which the sleeve moves during operation of the air spring. The hinge point at each sleeve end is axially outward from the adjacent support ring inner shoulder relative to the axial cross sectional line AL located at the maximum diameter of the sleeve when the air spring is at design height.
In another aspect of the invention, the air spring and rings may also be defined by the relationship of the maximum diameters of the sleeve and the rings at design height. At design height, the diameter of the support rings at the outer shoulder is greater than the maximum diameter of the sleeve.
The support rings may have a variety of configurations. The support ring may have a solid structure or may have a trough type configuration for reduced weight. The rings may be formed out of metals or thermoplastics or thermoresins. The rings may have a plurality of corrugated ribs to provide strength to the ring. The ring may have either an extending toe or an extending tab for fitment with the related bead rings. The ring may have any radially outwardly extending tab to assist the air spring in balance when the air spring is mounted. When the rings are employed with an air spring, the top and the bottom rings may have identical or differing configurations depending upon the desired air spring performance characteristics.